The invention relates to nanosized powders for applications such as structural, magnetic, catalytic, resistive and electronic, and bar coding applications.
Nanocrystalline materials such as nanocrystalline nickel have been reported to have uses such as wear resistant coatings, hydrogen storage materials, magnetic materials and catalysts for hydrogen evolution. See U.S. Pat. No. 5,352,266 wherein it is reported that nanocrystalline materials, nanophase materials or nanometer-sized crystalline materials can be prepared by sputtering, laser ablation, inert gas condensation, oven evaporation, spray conversion pyrolysis, flame hydrolysis, high speed deposition, high energy milling, sol-gel deposition and electrodeposition. In the field of catalysis, U.S. Pat. No. 5,547,649 discloses the use of nanocrystalline titania for hydrogen sulfide conversion.
Nanocrystalline materials have been reportedly made from metals (e.g., M50 type steel, Pd, Cu, intermetallics (e.g., Al52 Ti48)), semiconductors such as Si, metal carbonates such as ZnCO3, and metal oxides (e.g., SiO2, TiO2, Y2 O3, ZnO, MgO, Al2O3). See, for example, U.S. Pat. Nos. 5,580,655; 5,589,011; 5,695,617; 5,770,022; 5,876,683; 5,879,715; 5,891,548 and 5,962,132, the disclosures of which are hereby incorporated by reference. According to these patents, the production of nanocrystalline materials has been achieved by methods such as chemical synthesis, gas-phase synthesis, condensed phase synthesis, high speed deposition by ionized cluster beams, consolidation, high speed milling, deposition and sol-gel methods.
One method reported in the literature for the synthesis of intermetallic nanocrystalline material is mechanical ball milling. (Jartych E., et al., J. Phys. Condens. Matter, 10:4929 (1998); Jartych E., et al., Nanostructured Materials, 12:927 (1999); Amilis, X., et al., Nanostructured Materials 12:801 (1999); Perez R. J., et al., Nanostructured Materials, 7:565 (1996)). Jartych et al. report preparation of nanocrystalline powders of Fe-30 at. % Al, Fe-40 at. % Al and Fe-50 at. % Al by ball milling, all of which were found to possess strong ferromagnetic interactions. (Jartych E., et al., J. Phys. Condens. Matter, 10:4929 (1998); Jartych E., et al., Nanostructured Materials, 12:927 (1999)). However, the authors reported that even after 800 hours of milling time, small quantities of xcex1-Fe were still present in the samples as indicated by the hyperfine magnetic field distribution measurements. The presence of xcex1-Fe is believed to produce defects and high strain levels within the milled material. Amilis and coworkers reported that the microhardness of ball milled Fe-40Al at% alloy directly correlated with defect concentration. (Amilis, X., et al., Nanostructured Materials 12:801 (1999)). They reported possible media contamination during the process of ball milling, which resulted in the presence of low concentrations of SiO2 from the agate used for milling and presence of Fe3Al.
Perez and coworkers reportedly synthesized nanocrystalline Fe-10 at. % Al using cryogenic milling at liquid nitrogen temperature. (Perez, R. J., et al., Nanostructured Materials, 7:565 (1996)). The thermal stability of the milled material was found to be significantly higher than that of Fe milled under analogous conditions. The authors speculated that this increase in stability might be due to the formation of fine dispersoids of xcex3-Al2O3 or AlN, which would restrict the movement of the grain boundaries. In spite of the simplicity and efficiency of ball milling as a means by which nanocrystalline metallic alloys may be synthesized, there are some problems and limitations. For example, the microstructure of the milled products is very sensitive to the grinding conditions and may be unpredictably affected by unwanted contamination from the milling media and atmosphere. In addition, excessively long periods of milling time may be required. (Amilis, X., et al., Nanostructured Materials 12:801 (1999); Perez R. J., et al., Nanostructured Materials, 7:565 (1996)).
A process for manufacturing a magnetic core made of an iron-based soft magnetic alloy having a nanocrystalline structure is disclosed in U.S. Pat. No. 5,922,143. Nanocrystalline alloys having magnetic properties are also disclosed in U.S. Pat. Nos. 5,340,413 and 5,611,871. U.S. Pat. No. 5,381,664 discloses a nanocomposite superparamagnetic material that includes nanosized particles of a magnetic component (rare earth and transition element) dispersed within a bulk matrix.
In view of the state of the art of methods for preparing nanocrystalline powders, it would be desirable to develop uses of the nanocrystalline intermetallic powders in various fields of technology.
The present invention provides a variety of new uses for nanosized powders, the new uses utilizing advantageous and/or unique properties of such nanosized powders.
In one respect, the present invention provides intermetallic nanosized powders having a variety of applications. The powders can be made by techniques which provide control over the size, shape, and surface morphology of the nanoparticles that are produced.
Precise control of shape, size and surface morphology of materials at the nano scale level should serve as the underlying basis for building new high performance innovative materials that possess novel electronic, magnetic, and catalytic properties. Such materials are essential for technological advances in various fields of applications.